Wireless communication systems provide for radio communication links to be arranged within the system between a plurality of user terminals. Such user terminals may be mobile and may be known as “mobile stations,” “subscriber stations,” or “user equipment.” At least one other terminal, e.g. used in conjunction with subscriber stations, may be a fixed network equipment, e.g. a control terminal, base station, repeater, eNodeB, and/or access point. Such a system typically includes a system infrastructure which generally includes a network of various fixed terminals, which are in direct radio communication with the subscriber stations. Each of the base stations operating in the system may have one or more transceivers which may, for example, serve subscriber stations in a given local region or area, known as a “cell” or “site,” by radio frequency (RF) communication. The subscriber stations that are in direct communication with a particular fixed terminal are said to be served by the fixed terminal. In one example, all radio communications to and from each subscriber station within the system is made via respective serving fixed terminals. Sites of neighboring fixed terminals in a wireless communication system may be offset from one another or may be non-overlapping or partially or fully overlapping.
Wireless communication systems may operate according to an industry standard protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), or other radio protocols, the TETRA standard defined by the European Telecommunication Standards Institute (ETSI), the Digital Private Mobile Radio (dPMR) standard also defined by the ETSI, the Digital Mobile Radio (DMR) standard also defined by the ETSI, the Long Term Evolution (LTE) standard defined by the 3GPP, or the High Rate Packet Data (HRPD) standard defined by the 3GPP2. Communications in accordance with any one or more of these standards, or other standards, may take place over physical channels in accordance with one or more of a TDMA (time division multiple access), FDMA (frequency divisional multiple access), or CDMA (code division multiple access) protocol. Subscriber stations in wireless communication systems such as those set forth above send user communicated speech and data, herein referred to collectively as “traffic information,” in accordance with the designated protocol.
Many so-called “public safety” wireless communication systems provide for group-based radio communications amongst a plurality of subscriber stations such that one member of a designated group can transmit once and have that transmission received by all other members of the group substantially simultaneously. Groups are conventionally assigned based on function. For example, all members of a particular local police force may be assigned to a same group so that all members of the particular local police force can stay in contact with one another, while avoiding the random transmissions of radio users outside of the local police force. Due to the mission critical nature of the target users, such wireless communications system must provide high availability and reliability across varying geographic areas and radio environments.
In addition to public safety wireless communications systems, commercial wireless communications systems may provide services to retail or corporate customers via coverage areas adjacent to the public safety coverage areas, and/or coverage areas that partially or entirely overlap with public safety coverage areas. Public safety subscribers may also use commercial wireless communications systems for personal communications, business operations communications, or other types of communications. Commercial wireless communications systems may be configured, for example, to provide service levels commensurate with one of a plurality of various service package levels purchased by the customer.
Due to the mobile nature of subscriber stations, and the limited coverage range of any particular public safety wireless communications system, a particular public safety subscriber station may periodically or intermittently roam outside of a coverage area of a public safety wireless communications system. In order to address such possibilities, agreements may exist between the public safety wireless communication system operator and the commercial wireless communication system operator that allow the particular public safety subscriber to, at least temporarily, use the services of the commercial wireless communications system until the particular public safety subscriber station is able to move back into coverage of the public safety wireless communications system. Even in those cases where the public safety wireless communications system coverage area and the commercial wireless communications system coverage area overlap, the particular public safety subscriber station may choose to obtain service from the commercial wireless communications system due to, perhaps, insufficient or inconsistent signal quality for communications attempted with the public safety wireless communications system and an improved signal quality available at the commercial wireless communications system.
Situations may arise, however, due to the nature of the public safety subscriber station and its programmed functionality, that the particular public safety subscriber station may remain connected to the commercial wireless communications system and will find it difficult, if not impossible, to move back to the public safety wireless communications system, even when it is available and even when it may have a sufficient or even better signal than the commercial wireless communications system. This may occur, for example, in those protocols such as LTE that maintain an active connection between the subscriber station and the communications system when persistent background data transfers continue to occur, such as in the transmission of periodic location updates often transmitted by public safety subscriber stations to ensure that commanders, dispatchers, and other group members or interested parties are always aware of the public safety subscriber station's most recent location. Similar problems may arise in other protocols and air-interfaces, and for other types of subscriber stations.
Unfortunately, the public safety subscriber station may not be granted the same prioritized signaling permissions, or the same elevated quality of service (QoS) levels, when operating in the commercial wireless communications system that would be granted to it by the public safety wireless communications system, and based on service level packages offered on the commercial wireless communications system, may be granted a lower priority than other commercial subscriber stations operating on the commercial wireless communications system. Furthermore, some agreements provide for remuneration to the commercial wireless communications system operator for any services provided to the particular public safety subscriber station, which could result in substantial charges if the particular public safety subscriber station remains connected to the commercial wireless communications system. Accordingly, there is a need for a solution that would allow the particular public safety subscriber station to selectively detach from the commercial wireless communications system and re-attach to an available public safety wireless communication system (perhaps made available due to movement of the particular public safety subscriber station or due to improved radio environments), thereby improving service quality provided to the particular public safety subscriber station and reducing the charges incurred while roaming in the commercial wireless communications system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.